I'm not sure if that really qualifies as a bug, but it is definitely not the way things should work.
I had a land caravan coming to my settlement, and while they were staying to trade, one of their Muffalos died of heart attack (of old age probably). And as a result, all the loot it was carrying - including over 2k silver - just dropped for my grabs and none of traders seemed to object.
A quick solution for this could be tweaking a generator for land caravans to make sure all Muffalos can survive the trip - like don't generate Muffalos older than 5 years or something.
Another solution might be adding a behavior to traders allowing them to grab any unclaimed item they find in a certain area around them and drop all items from dead Muffalo as unclaimed.
Or you could extend the claiming system, making items to possibly belong to other factions (like if you have a claiming value 0 for unclaimed and 1 for owned, you can add negative codes of factions to mark if a faction owns it). and if you claim an item that belongs to a faction this will worsen your relation with them.
Yeah I think it would make more sense if they could pick up items dropped by their pack muffalos. Thanks for the suggestion.